Maternal serum alpha-fetoprotein screening after chorionic villus sampling.

To evaluate whether maternal serum alpha-fetoprotein (MSAFP) concentrations at 15-18 weeks' gestation are influenced by chorionic villus sampling performed three to ten weeks earlier, MSAFP levels were determined for 417 postchorionic villus sampling patients and 967 control subjects without previous chorionic villus sampling. Statistical comparison of the medians, distributions, and proportions above defined multiples of the median demonstrated no significant difference between the two populations. These results indicate that MSAFP screening in postchorionic villus sampling patients should be reliable and that values may be interpreted using criteria similar to those used for the general population.

Familial aggregation of periodontal indices.

Analysis of three measures of periodontal health (plaque index, gingival index, and attachment loss) was carried out on 178 individuals in 75 families examined as part of a family study of periodontal health. Original participants in this study were volunteers recruited from the University of Maryland Dental Clinic, and were selected independently of any specific dental disease or condition. Relatives were invited to participate in the family study so that the extent of familial aggregation of indices of periodontal health could be assessed. By means of an analysis of variance model for persons nested within families, evidence for familial aggregation of plaque index was found both before and after adjustment for covariates such as age, gender, race, and reported oral hygiene habits. While a substantial fraction of variance in gingival index and attachment loss was also due to differences among families, neither attained statistical significance in these data. Examination of familial correlations (e.g., parent-offspring, sib-sib, spouse correlations) confirmed that plaque index showed greater familial resemblance compared with other measures of periodontal health. Both mean gingival index and mean attachment loss showed a stronger correlation between mothers and offspring compared with fathers and offspring. This suggests that further analysis of models for separating genetic and environmental effects may be appropriate for plaque index, but complete analysis of other periodontal indices will require more flexible statistical models for separation of genetic and cultural inheritance while considering gender-specific expression and transmission, as well as incorporation of information from covariates.

Genetics of total serum IgE levels: a regressive model approach to segregation analysis.

The genetics of basal total serum IgE levels was investigated in 278 individuals from 42 randomly ascertained nuclear families. The data were analyzed using the regressive model approach to segregation analysis with age, sex, and a measure of skin test responsiveness as covariates in the Class D models. The best fitting model was that of recessive inheritance of high IgE levels with a gene frequency of 0.99 for the "high" allele. Only 3 families showed evidence for segregation of the rare "low" allele, and, if extended further, these families could be useful for molecular genetic linkage studies. These results suggest that there may be a rare allele for very low total serum IgE levels that can be detected even after a measurement of allergic responsiveness (skin test results) is considered as a covariate. Therefore, this major gene for IgE levels appears independent of any similar locus controlling atopy.

Alphoid DNA polymorphisms for chromosome 21 can be distinguished from those of chromosome 13 using probes homologous to both.

Although alphoid DNA sequences shared among acrocentric chromosomes have been identified, no human chromosome 21-specific sequence has been isolated from the centromeric region. To identify alphoid DNA restriction fragment length polymorphisms (RFLPs) specific for chromosome 21, we hybridized human genomic DNA with alphoid DNA probes [L1.26; aRI(680),21-208] shared by chromosomes 13 and 21. We detected RFLPs with restriction enzymes ECoRI, HaeIII, MboI,StuI, and TaqI. The segregation of these RFLPs was analyzed in the 40 CEPH families. Linkage analysis between these RFLPs and loci previously mapped to either chromosome 13 or 21 revealed RFLPs that appear to be specific to chromosome 21. These polymorphisms may be useful as genetic markers of the centromeric region of chromosome 21. Different alphoid loci within the centromeric region of chromosome 13 were identified.